diff --git a/src/Compilers/CSharp/Test/Syntax/Diagnostics/DiagnosticTest.cs b/src/Compilers/CSharp/Test/Syntax/Diagnostics/DiagnosticTest.cs
index e24f495665bdd..ffc6e4ad098c9 100644
--- a/src/Compilers/CSharp/Test/Syntax/Diagnostics/DiagnosticTest.cs
+++ b/src/Compilers/CSharp/Test/Syntax/Diagnostics/DiagnosticTest.cs
@@ -349,7 +349,6 @@ public void WarningLevel_2()
                         case ErrorCode.WRN_InterpolatedStringHandlerArgumentAttributeIgnoredOnLambdaParameters:
                         case ErrorCode.WRN_CompileTimeCheckedOverflow:
                         case ErrorCode.WRN_MethGrpToNonDel:
-                        case ErrorCode.WRN_AnnotationOnSliceReturnType:
                             Assert.Equal(1, ErrorFacts.GetWarningLevel(errorCode));
                             break;
                         case ErrorCode.WRN_InvalidVersionFormat: